Process of producing chromates



March 21, 1933. J. J. VETTER PROCESS -OF PRODUCING CHROMATES 1930 2 Sheets-Sheet 2 Filed July 5 INVENTOR ATTORNEY Patented Mar. 21, 1933 UNITED STATES PATENT OFFICE JOSEPH J. VETTER, 0F HACKEN SACK, NEW JERSEY, ASSIGN'OB TO NATURAL PRODUCTS REFINING (30., OF JERSEY CITY, NEW JERSEY, A CORPORATION OF DELAWARE PROCESS OF PRODUCING CHROMATES Application filed July 3,

My invention relates to a process of producing chromatesfrom any suitable materials containing chromium, but relates especially to a treatment of chrome ores such as are used in the manufacture of chromates.

The object of my invention is to provide a process of the above character, having many advantages over previous processes used for this purpose. More especially, the object of my invention is to provide a process whereby larger yields of chromates may be obtained and preferably in accordance with a pro cedure involving lower costs. My process involves, also, the use of a shorter time in the production of products therein. Also, my process may be carried out in such a way, if desired, so as to obviate one of the steps of leaching, thus obviating after the first roasting, the necessity of filtration with its accompanying disadvantages, and consequently obviating the necessity of re-weighing, re-mixing and drying in the course thereof. Nhen carried out in this way, the process may include in the course of the same a grinding operation which enables further oxidation of the partially treated product to be attained, in view of the fact that the lumps formed in the process are broken up, thus presenting new surfaces therein for the action thereon by the materials added.

Hitherto the process for producing chromates from chrome ore necessitated a considerable number; of steps and have involved the addition of either a very large amount of basic refractory material such as lime or such a small amount of the basic refractory material, as to not attain a particularly high yield of the chromate, also a step of leaching, involving subsequent filtration, weighing, mixing and drying, preliminary to a retreatment of the partly treated ore, all of which have involved great expense which I find unnecessary and undesirable.

Further objects of my invention will appear from the detailed description of the same hereinafter. I

While my invention is capable of embodiment in many difierent forms, I have described hereinafter only certain forms of my invention, by way of example, and while it is 1920. Serial No. 465,683.

capable of being carried out in a great many difierent types of apparatus, I have shown only certain forms of apparatus for use in connection therewith in the accompanying drawings, in which:

Fig. 1 is a diagrammatic representation of an apparatus which may be used in accordance with my invention;

Fig. 2 is a vertical section of the kiln used in accordance with my invention;

Fig. 3 is a diagrammatic representation of the steps of one form of my invention;

Fig. 4 is a diagrammatic representation of the steps in a modified form of my invention; and

Fig. 5 is an enlarged cross sectional detail.

Referring to the drawings, I have shown an apparatus comprising an elongated inclined rotary kiln 1, preferably about 10 to 13 times the inside diameter thereof, having any suitable lining 2, and carried upon cylindrical tracks 3 and 1, which are supported upon rollers 5 and 6. The inclined rotary kiln 1 may be driven from any suitable source of power as, for example, by means of a gear 7, carried by the kiln, which meshes with a driving gear 8 connected to any motive power as desired. At its upper end the kiln may be supplied continuously with materials to be treated therein through a hopper 9, having an outlet 10 extending into the kiln. At its lower end there extends into the kiln an elongated burner tube 11 located in an air supply controlling tube 11a provided with a head having air ports 11?) movable by a hand wheel 11c screw-threaded thereto and splined in an air tube 11d having a valved air supply lle extending for a distance of about to the length of the kiln, the kiln having a length of about 10 to 18 times the inside diameter thereof. The oil pipe 11 may be supplied with any desired fuel as, for example, gas, but preferably with crude oil which is burned at the inner end of the burner 11 by means of a spray nozzle 12 of any desired type. A pipe 13 of heat resisting steel is located around the burner tube 11 upon asupport 13a in such a manner that the outer end thereof draws in a current of air while the inner end of said pipe 13 is so arranged as to permit the escape of the air in proximity to the spray nozzle 12 in order to provide oxygen for the combustion of the fuel within the kiln. The burner 12 and pipe 13 are supported within a kiln Q hood 136, having angle adjusting screw supports 130. These are supported from adjustable screw sleeves 13d carried by turnbuckles 130 from rollers 13f movable on a cross beam 1239' supported on any suitable uprights 1871, and 135 longitudinally adjustable on tracks 181' and 1370.

The resultant material escapes from the lower end of the rotary kiln 1 preferably in advance of the end of the shield pipe 13. However, due to the upward fiow of the burning fuel and the incoming air there is also a current of air entering the lower end of the kiin 1 and passing upwardly through the same outside of the shield tube 13. This arrangement is such as to provide a cooling zone for the downwardly moving materials around the tube 11 and pipe 18 in which the incoming air not only cools the materials passing downwardly therein, but also becomes heated, thereby assisting in the oxidation of the said materials throughout the kiln 1.

In carrying out my invention, for example, I might introduce into the kilnl through the hopper 9 a mixture of finely groimd chrome ore containing, for instance:

100 parts by weight chrome ore (containing (lr O parts by weight of lime 19 parts by weight of soda ash In this mixture the lime may, however, vary from 70 parts to parts by weight and, if desired, the soda ash may vary from 45 parts to 53 parts by weight. Also, the lime may be any other basic refractory material and the soda ash may be substituted wit-h any other alkali carbonate. It will be understood, also, that in this application wherever I refer to lime or soda ash such substitute materials may be used if desired. This amount of basic refractory material is at least such as not only to prevent the formation of any undesirable compounds from the soda ash and the silica and alumina which is contained in the chrome ore, but is suflicient also to attain the high yields of chromates hereinafter referred to. Also, the soda ash is present in sufiicient quantity to combine with somewhat less than, that is to say, about 7 0% by weight of the ehromic oxide present. This m'xture is roasted in the kiln at a temperature of about 1000 C., in the oxidizing atmosphere present therein in the upper part of the kiln, that is to say, between the upper end of the burner 12 and the upper end of the kiln, after which the materials pass downwardly into the cooling zone, that is to say, between the upper end of the burner and the lower end of the kiln in which the average temperature is approx- 65 imately 800 6., so that the materials pass out the lower end of the kiln at a temperature of about 600 C. The reactions which take place in the kiln 1 are as follows:

CaClOg CaO CO 2(FeO Cr O 1CaO+70 4(Ca0 CrO +Fe O 2 (FeO C150 +t(Na O CO l-(Na O C10 +Fe O +4CO The treatment in the kiln 1 requires approximately 3 hours.

These materials delivered from the kiln 1 are in the form of particles varying in size from a fine powder to lumps 1 inch in diameter, the latter having been oxidized practi- 'ca ly only at the surface thereof, and containing calcium ehromate, sodium chromate as well as the silicates of lime and alumina. These materials may be then subjected to a leaching operation in water, containing uneombin ed sodium carbonate to decompose calcium ehromate so as to form sodium chromate therefrom for a period of 2% hours, and is then filtered through any desired apparatus, the liquid which contains sodium eliminatebeing then evaporated or treated in any desired manner for the recovery of sodium chromate or sodium bichromate therefrom, according to the usual procedure. The leaching operation is preferably conducted at a temperature of 80 (1, and requires a period generally of 12 hours. The residue thus recovered from the filter is ground either wet or dry while mixed with enough soda ash which is added thereto in an amount either to combine with somewhat less than the total chromic oxide present therein, that is to say, to combine with about 90% by weight of the chromic oxide present, or more up to an amount equal to about of the theoretieal soda ash required to combine therewith. For example, this mixture may comprise 100 parts by weight of the dry residue (containing approximately 12% by weight C and 15 parts by weight of soda ash. although the soda ash may vary from 12 parts to 20 parts by weight of said residue. This mixture is hen re-roasted in substantially the same way and under the same conditions as the first roasting operation in the kiln 1. The ma- 7-115 terials thus obtained f 'om the re-roasting may then be subjected also to leaching, filtration and evaporation in substantially the same way as described above after the first roasting. By this means I am enabled to obtain .320 a very high yield of the alkali chromate, inasmuch as a recovery corresponding to from 90% to 95% by weight of the chromic oxide present in the original chrome ore is recovered in the form of the alkali chromate 01- bichromate. about of this amount having been recovered from the first leaching following the first roasting operation.

If desired, however, I may conduct the process in such a manner as to enable a very much lower cost of production to be attained and in a much shorter interval of time, as follows:

In this modification of my invention the process may be carried out in a manner somewhat similar to the form of my invention described in detail above. However, in this instance I prefer to mix together 100 parts by weight of chrome ore (containing about 50% by weight of 01:20,) parts by weight of lime 63 parts by weight of soda ash.

Here, if desired, the lime or other basic refractory material may vary from 70 parts to parts by weight and the soda ash or other alkali carbonate may vary from 60 parts to 66 parts by weight of the chrome ore. Here it will be noted that the amount of soda ash present is sufiicient to combine with about by weight of the total chromic oxide present in the ore. This mixture is then passed through the kiln 1 under the same conditions of operation until the oxidation of the chromic oxide is from 60% to 70% by weight completed. At this stage of the process no leaching operation is necessary. Instead, preferably, the materials thus treated, the same being in the form of a fine powder up to lumps 1 inch in size, are ground to a fine powder and then run again through the kiln 1 under substantially the same conditions of operation and without the necessity of adding any further lime or soda ash thereto. The materials thus treated are then sub jected to a leaching operation under the same conditions of treatment referred to in the first leaching hereinabove described in connection with the first embodiment of my invention, after which the filtrate is evaporated to obtain sodium chromate, or bichromate and the residue may then be discarded. The yield of sodium chromate or bichromate thus ob tained corresponds to a recovery of from 88% to 92% by weight of the chromic oxide present in the chrome ore treated.

WVhile I have described my invention above in. detail it is to be understood that many changes may be made therein without departing from the spirit of my invention as set forth in the claims.

I claim:

1. The process which comprises roasting chrome ore with a basic refractory material and an alkali carbonate then grinding the product, re-roasting the said unleached prod not and recovering the alkali chromate therefrom.

2". The process which comprises roasting chrome ore with a basic refractory material and an alkali carbonate, then grinding the product, re-roasting the said unleached product and recovering the alkali chromate therefrom by leaching, filtration and evaporation.

3. The process which comprises roasting JOSEPH J. VETTER. 

